Optical Phase Conjugation in a Silicon Waveguide With Lateral p-i-n Diode for Nonlinearity Compensation

In-line optical phase conjugation is a well-known technique to enhance the received signal quality through nonlinearity compensation. Being able to implement the conjugation in cm-scale highly nonlinear devices, which can be integrated on a silicon chip, could potentially lead to several benefits in terms of small footprint and cointegration with linear signal processing functionalities, as well as lower power consumption. Here, we focus on silicon waveguides to implement the optical phase conjugation through four-wave mixing. The challenges in terms of conversion efficiency imposed by the presence of nonlinear loss are tackled by using a lateral p-i-n diode along the waveguide. When the diode is reverse biased, the conversion efficiency can be effectively enhanced by the decrease in free-carrier absorption. Low-penalty conversion can therefore be achieved for wavelength-division multiplexing (WDM) signals and the high quality of the generated idlers is critical in demonstrating a 1-dB Q-factor improvement through optical phase conjugation in a 5-WDM channel 16-QAM transmission system after 644 km of dispersion-compensated transmission. The performance improvement enables a performance better than the hard-decision forward error correction threshold for all the transmitted channels.